Planar surface illuminator

ABSTRACT

A planar surface illuminator ( 20 ) for installation below a liquid crystal display panel includes a light guide plate ( 22 ) and a plurality of point light sources ( 21 ). The light guide plate has a bottom surface ( 223 ), an end surface ( 221 ) and a number of dot-patterns ( 23 ) formed on the bottom surface. The point light sources are positioned adjacent the end surface to irradiate the light guide plate. Darkened areas ( 223   a ) between the point light sources are lightened by placing special dot-patterns ( 23   a ) therein, which special dot-patterns are made of melamine-based fluorescent particles. The melamine-based fluorescent particles function as many small light sources, thus lightening the darkened areas. Therefore, the brightness of the planar surface illuminator is thereby balanced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a planar surface illuminator,and especially to a planar surface illuminator using point sources andprovided below a liquid crystal display (LCD) panel.

[0003] 2. Description of the Related Art

[0004] Most users expect displays in portable devices, such as laptopand notebook computers, mobile phones and game devices, to have large,clear, bright viewing screens, equaling the performance of thecathode-ray-tube (CRT) monitors sitting on their desks. LCDs are onetype of FPD which satisfies these expectation. But because liquidcrystals are not self-luminescent, LCDs need a planar surfaceilluminator which offers sufficient luminance (brightness) in a planarsurface. Typically, planar surface illuminators have one of two types oflight sources, one being linear sources, such as a cold cathodefluorescent lamp (CCFL), and the other being point sources, such aslight emitting diodes (LED). Different types of light sources requiredifferent planar surface illuminator design structures.

[0005] As shown in FIG. 5, a conventional planar surface illuminator 10which uses point light sources comprises a light guide plate 15 andthree point sources 13 positioned at one side of the light guide plate15. The light guide plate 15 couples with light beams emitted from thepoint sources 13 to create a planar surface illuminator for irradiatinga liquid crystal panel (not shown). The point sources 13 are LEDs, eachof which has an emission beam of Gauss beam. The Gauss beam has anoptical intensity distribution function shaped like a Gauss curve.

[0006] In operation, the Gauss beams from the LEDs irradiate an endsurface (not labeled) of the light guide plate 15, and may transmit inthe light guide plate 15 or may be emitted out of the light guide plate15 through an output surface (not labeled), which is perpendicular tothe end surface. As seen in FIG. 5, a lower intensity part of the Gaussbeams illuminates the areas D, E, F, G between and adjacent each twoLEDs, just there, so much so that in some areas near the mid-point ofeach two LEDs, almost no beams are emitted therefrom. Therefore,darkened areas are formed near points D, E, F, and G. Therefore, theplanar surface illuminator can not produce a uniform brightness over anarea of the liquid crystal display panel.

SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the present invention is to provide aplanar surface illuminator which provides a more uniform brightness to aliquid crystal display panel.

[0008] Another object of the present invention is to provide a planarsurface illuminator which more efficiently utilizes the light energy ofpoint light sources.

[0009] To achieve the above objects, a planar surface illuminator forplacement below a liquid crystal display panel comprises a light guideplate and a plurality of point light sources. The light guide plate hasa bottom surface, an end surface and a number of dot-patterns formed onthe bottom surface. The point light sources are positioned at the endsurface to irradiate the light guide plate. Darkened areas between thepoint light sources are lightened by placing special dot-patternstherein, which special dot-patterns are made of melamine-basedfluorescent particles. The melamine-based fluorescent particles functionas many small light sources, thus lightening the darkened areas.Therefore, the brightness of the planar surface illuminator is therebybalanced and made more uniform.

[0010] Other objects, advantages and novel features of the presentinvention will be apparent from the following detailed description ofpreferred embodiments thereof with reference to the attached drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of a planar surface illuminatorconstructed in accordance with a preferred embodiment of the presentinvention from a bottom-side aspect;

[0012]FIG. 2 is a bottom plan view of FIG. 1;

[0013]FIG. 3 is a greatly magnified view of a small portion of a specialdot-pattern for use in the darkened areas of FIG. 2;

[0014]FIG. 4 is a bottom plan view of a planar surface illuminatorconstructed in accordance with a second preferred embodiment of thepresent invention; and

[0015]FIG. 5 is a perspective view of a conventional planar surfaceilluminator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Referring to FIG. 1, a planar surface illuminator 20 forinstallation below a liquid crystal display panel (not shown) comprisesa light guide plate 22 and a plurality of point light sources 21. Thepoint light sources 21 are positioned to a side of the optical lightguide plate 22. Light from the point light sources 21 couples with anoptical input surface 221 of the optical light guide plate 22.

[0017] Similar to the point sources 12 shown in FIG. 5 with theconventional planar surface illuminator 10, the point sources 21 in FIG.1 are LEDs, each of which has an emission beam of Gauss beam. The Gaussbeam has an optical intensity distribution function shaped like a Gausscurve. In operation, the Gauss beams from the LEDs irradiate the inputsurface 221 of the light guide plate 22, and may transmit in the lightguide plate 22, or may be emitted out of the light guide plate 22 froman output surface 222 which is perpendicular to the input surface 221.Absent connective structure, the result would be formation of darkenedareas 223 a adjacent and in between each two LEDs.

[0018] The optical light guide plate 22 is shaped substantially as arectangular plane plate and comprises the optical input surface 221adjacent to the light sources 21, the optical output surface 222, abottom surface 223, and three side surfaces 224. The input surface 221defines grooves (not labeled) corresponding to each point light source21. Alternatively, the optical light guide plate 22 can be substantiallyshaped as a wedge. To improve optical performance efficiency, reflectivesheets or films (not shown) can be secured on the bottom surface 223 andthe three side surfaces 224. The use of the reflective sheets or filmsensures that virtually all the optical light beams from the lightsources 21 are eventually emitted from the optical output surface 222.

[0019] Referring also to FIGS. 2 and 3, a number of reflectivedot-patterns 23 are formed on or applied to the bottom surface 223 in auniform pattern to promote uniform emission of light from the opticaloutput surface 222. Note that the dot-pattern 23 are all of a same sizein a same column, but increase in size in a same now as a distance awayfrom the optical input surface 221 increases. The dot-patterns 23 areinjection molded or printed on the bottom surface 223. To balance lackof illumination emitted from the darkened areas 223 a and thereby toprovide an even brightness to the liquid crystal display panel, somedot-patterns 23 a positioned in the darkened areas 223 a specially aremade of melamine-based fluorescent particles 25 (see FIG. 3). Thedot-patterns 23 a constitute the connective structures referred toabove. Diameters of the melamine-based fluorescent particles 25 are in arange of from 1 to 10 microns. So as to corresponded to differentemission wavelengths of the LEDs. Each melamine-based fluorescentparticle 25 can be a mixture or one of green, red and orange fluorescentdyes polymerized with melamine particles. Excitation and emissionwavelengths of the green fluorescent dyes are respectively about 506 and529 nanometers; excitation and emission wavelengths of the redfluorescent dyes are respectively about 636 and 686 nanometers, andexcitation and emission wavelengths of the orange fluorescent dyes arerespectively about 560 and 584 nanometers.

[0020] In operation, when exited by light beams from the LEDs 21, themelamine-based fluorescent particles 25 function as many small lightsources lighting the darkened areas 223 a, and so the brightness of theplanar surface illuminator 20 is balanced. Furthermore, light beams fromthe melamine-based fluorescent particles 25 do not lighten the darkenedareas 223 a only, they also transmit into or out of other areas of thelight guide plate 22, the optical energy of the LEDs are adequatelyutilized. The total brightness, therefore, is also increased.

[0021] Turning to FIG. 4, the dot-patterns 23 also can be uniformlyspaced on the bottom surface 223, with all the dot-patterns 23 being ofthe same size. The special dot-patterns in the darkened areas 223 a arenot made of melamine-based fluorescent particles 25, it just be coatedwith melamine-based fluorescent particles, it also can provide evenbrightness to the liquid crystal display.

[0022] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A planar surface illuminator for use beneath a liquid crystal displaypanel comprising: a light guide plate comprising a bottom surface; aplurality of point light sources irradiating the light guide plate,darkened areas of the light guide plate being formed adjacent to thepoint light sources; and a number of dot-patterns formed on the bottomsurface, wherein some dot-patterns positioned at the darkened areas aremade of melamine-based fluorescent particles.
 2. The planar surfaceilluminator as described in claim 1, wherein the melamine-basedfluorescent particles are polymerized with green fluorescent dye andmelamine particles.
 3. The planar surface illuminator as described inclaim 2, wherein excitation and emission wavelengths of the greenfluorescent dye are respectively about 506 and 529 nanometers.
 4. Theplanar surface illuminator as described in claim 1, wherein themelamine-based fluorescent particles are polymerized with redfluorescent dye and melamine particles.
 5. The planar surfaceilluminator as described in claim 4, wherein excitation and emissionwavelengths of the red fluorescent dye are respectively about 636 and686 nanometers.
 6. The planar surface illuminator as described in claim1, wherein the melamine-based fluorescent particles are polymerized withorange fluorescent dye and melamine particles.
 7. The planar surfaceilluminator as described in claim 6, wherein excitation and emissionwavelengths of the orange fluorescent dye are respectively about 560 and584 nanometers.
 8. The planar surface illuminator as described in claim1, wherein each melamine-based fluorescent particle is a mixture ofgreen, red and orange fluorescent dyes polymerized with melamineparticles.
 9. The planar surface illuminator as described in claim 1,wherein diameters of the melamine-based fluorescent particles are in arange of from 1 to 10 microns.
 10. The planar surface illuminator asdescribed in claim 1, wherein the dot-patterns are uniformity spaced onthe bottom surface.
 11. The planar surface illuminator as described inclaim 1, wherein the dot-patterns are uniformly spaced on the bottomsurface, and the further the dot-patterns are away from the pointsources, the larger the diameter of the dot-patterns are.
 12. The planarsurface illuminator as described in claim 1, wherein the dot-patternsare injection molded or printed on the bottom surface.
 13. The planarsurface illuminator as described in claim 1, wherein the point lightsources are light emitting diodes.
 14. The planar surface illuminator asdescribed in claim 1, wherein the point light sources are positioned atone side of the light guide plate.
 15. A planar surface illuminator foruse beneath a liquid crystal display panel comprising: a light guideplate comprising a bottom surface; a plurality of point light sourcesirradiating the light guide plate, darkened areas of the light guideplate being formed adjacent to the point light sources; and a number ofdot-patterns formed on the bottom surface, wherein some dot-patternscoated with melamine-based fluorescent particles are positioned at thedarkened areas, for providing even brightness to the liquid crystaldisplay.
 16. The planar surface illuminator as described in claim 15,wherein the melamine-based fluorescent particles are polymerized withgreen fluorescent dye and melamine particles.
 17. The planar surfaceilluminator as described in claim 16, wherein excitation and emissionwavelengths of the green fluorescent dye are respective about 506 and529 nanometers.
 18. The planar surface illuminator as described in claim15, wherein the melamine-based fluorescent particles are polymerizedwith red fluorescent dye and melamine particles.
 19. A planar surfaceilluminator for use beneath a liquid crystal display panel, comprising:a light guide plate defining a side face, a bottom face and a top faceopposite to said bottom face; a plurality of point light sources locatedby the side face and spaced from one another along said side face undera condition that each of said point light sources defines effectivelight exposure within a specific sector range so as to result in areaswith thereof different brightness where the brighter areas are exposedunder more effective light exposure while the darker areas are exposedunder less effective light exposure; and a plurality of dot-patternsformed on the bottom face; wherein only some of said dot-patterns, whichare essentially located in the darker areas, are equipped withfluorescent particles whereby uniform emission is obtained on the topface.